14 ISLAND LIFE 



continuous distribution of a species, there being a gap of 

 about a thousand miles between its southern limits in 

 Russia, and its reappearance in the Alps. There are of 

 course numerous instances in which species occur in two 

 or more islands, or in an island and continent, and are thus 

 rendered discontinuous by the sea, but these involve 

 questions of changes in sea and land which we shall have 

 to consider furtlier on. Other cases are believed to exist 

 of still Avider separation of a species, as with the marsh 

 titmice and the reed buntings of Euro23e and Jaj^an, where 

 similar forms are found in the extreme localities, while 

 distinct varieties or sub-sj^ecies, inhabit the intervening 

 districts. 



Extent and Limitations of Speeijic Areas. — Leaving for 

 the present these cases of want of continuity in a species, 

 we find the most wide difference between the extent of 

 country occupied, varying in fact from a few square miles 

 to almost the entire land surface of the globe. Among 

 the mammalia, however, the same species seldom inhabits 

 both the old and new worlds, unless they are strictly arctic 

 animals, as the reindeer, the elk, the arctic fox, the glutton, 

 the ermine, and some others. The common wolf of Europe 

 and Northern Asia is thought by many naturalists to be 

 identical with the variously coloured wolves of North 

 America extending from the Arctic Ocean to Mexico, in 

 which case this will have perhaps the widest range of any 

 species of mammal. Little doubt exists as to the identity 

 of the brown bears and the beavers of Europe and North 

 America; but all these species range up to the arctic 

 circle, and there is no example of a mammal universally 

 admitted to be identical yet confined to the temperate 

 zones of the two hemispheres. Among the undisjDuted 

 species of mammalia the leopard has an enormous range, 

 extending all over Africa and South Asia to Borneo and 

 the east of China, and thus having probably the widest 

 range of any known mammal. The winged mammalia 

 have not usually very wide ranges, there being only one 

 bat common to the Old and New Worlds. This is a 

 British sjiecies, Vesperugo serotinus, which is found over 

 the larger part of North America, Europe and Asia, as far 



